Poly(vinyl fluoride) (PVF) is used in film form for a variety of protective and decorative applications.
The polymerization of vinyl fluoride (VF) has typically been carried out in water by means of a water soluble initiator such as 2,2'-azobis(isobutyroamidine) dihydrochloride to yield a highly fluid aqueous dispersion or slurry of very finely divided polymer particles. Polymerizations of this type, in which the initiator is water soluble and the monomer has limited water solubility, are often termed emulsion polymerizations. It is well known in the art of emulsion polymerization that the addition of surface active substances, or emulsifiers, the molecules of which are composed of hydrophilic and hydrophobic segments, improve the polymerization process. The improvement may be accomplished by better distribution of monomer within the aqueous phase, making it more available to the initiator, thus facilitating polymerization, or by stabilizing the dispersion of polymer particles, allowing more concentrated slurry to be produced without formation of large polymer agglomerations, or by a combination of both effects. The use of an emulsifier, therefore, offers advantages in productivity and economics.
The emulsifier, may, in general, have a hydrophilic segment that is cationic, anionic or nonionic in nature, while the hydrophobic segment is often alkyl or alkaryl in nature. To be compatible with 2,2'-azobis(isobutyroamidine) dihydrochloride the emulsifier cannot be anionic in nature lest it form an insoluble complex salt with the initiator. Such salts have been found to be ineffective initiators for the polymerization process. A variety of nonionic and cationic emulsifiers are commercially available and are known to be useful in emulsion polymerization. Examples of many such materials are described in D. C. Blackley, "Emulsion Polymerization", Halsted Press, New York, N.Y., 1975, pp 308-318. The nonionic materials almost invariably contain hydrophilic segments derived from oligomers of ethylene oxide. While these emulsifiers are compatible with the 2,2'-azobis(isobutyroamidine) dihydrochloride initiator, they invariably produce low yields of low molecular weight PVF products that are not useful in typical applications for PVF. Common cationic emulsifiers such as dodecylammonium chloride or cetyl pyridinium chloride, specified by Blackley as useful in polymerizations for producing positively charged particles, are compatible with 2,2'-azobis(isobutyroamidine) dihydrochloride but produce PVF of low molecular weight in reduced yields and often contribute a highly undesirable yellow or brown color to the polymer. As such, none of these emulsifiers are suitable for emulsion polymerization of VF. Other cationic emulsifiers such as C.sub.6 F.sub.13 CH.sub.2 CH.sub.2 SCH.sub.2 CH(OH)CH.sub.2 N(CH.sub.3).sub.3 Cl, manufactured by Ciba Geigy and offered under the tradename Lodyne.RTM. S-106A, have similarly been found to inhibit polymerization and produce low molecular weight PVF.